Serotonin is a compound contained abundantly in platelets, which are a blood component, and in a central nervous system, it acts as a neurotransmitter. In platelets, it is released upon stimulation by thromboxane A2, ADP, collagen or the like, and synergistically acts on release of various platelet aggregation factors through activation of serotonin-2 receptors in the platelets and vascular smooth muscle cells and also on vasoconstriction by norepinephrine through α1 receptors, thereby inducing strong platelet aggregation and vasoconstriction [P. M. Vanhoutte, “Journal of Cardiovascular Pharmacology”, Vol. 17 (Supple. 5), S6–S12 (1991)].
Serotonin is also known to potentiate proliferation of vascular smooth muscle cells [S. Araki et al., “Atherosclerosis”, Vol. 83, pp. 29–34 (1990)]. It has been considered that, particularly when endothelial cells are injured as in arteriosclerosis or myocardial infarction, the vasoconstricting action and thrombus forming action of serotonin are exasperated, thereby reducing or even stopping blood supply to myocardial, cerebral and peripheral organs [P. Golino et al., “The New England Journal of Medicine”, Vol. 324, No. 10, pp. 641–648 (1991), Y. Takiguchi et al., “Thrombosis and Haemostasis”, Vol. 68(4), pp. 460–463 (1992), A. S. Weyrich et al., “American Journal of Physiology”, Vol. 263, H349–H358 (1992)]. Being attracted by such actions of serotonin or serotonin-2 receptors, various attempts are now under way to use a serotonin-2 receptor antagonist as a pharmaceutical for ischemic diseases of the heart, the brain and peripheral tissues.
Several compounds, led by sarpogrelate, are known to have serotonin-2 receptor antagonistic action. They however do not include anything having the pyrrolo[2,3-e][1,2]thiazine skeleton, pyrrolo[3,4-e][1,2]thiazine skeleton, pyrrolo[2,3-f][1,2]thiazepine skeleton or pyrrolo[3,4-f][1,2]thiazepine skeleton. Those known to have serotonin-2 receptor antagonistic action are accompanied with many problems to be improved in potency, toxicity, side effects or the like. On the other hand, medicines which have anti-serotonin action and α1-blocking action in combination are considered to become extremely effective medicines for the treatment and prevention of hypertension and ischemic heart diseases, because they have possibility to reduce side effects, such as orthostatic hypotension and reflex tachycardia, induced by antihypertensive action on the basis of the α1-blocking action and hypertension is a serious risk factor for ischemic heart diseases.